RELATIONSHIP OF SPECIFIC LEAF AREA AND CARBON ISOTOPE DISCRIMINATION WITH DRY MATTER PRODUCTION AND POD YIELD IN GROUNDNUT GENOTYPE UNDER MOISTURE STRESS

RELATIONSHIP OF SPECIFIC LEAF AREA AND CARBON ISOTOPE

DISCRIMINATION WITH DRY MATTER PRODUCTION AND POD YIELD IN

GROUNDNUT GENOTYPE UNDER MOISTURE STRESS

M. ASALATHA, P. V. REDDY AND RAMAN A RAO, D. V.

Regional Agriculture Research Station, Timpati-517 507, A.P. Received on 18 Nov., 1998, Revised on 24 July, 1999

SUMMARY

The relationship of specific leaf area and carbon isotope discrimination with dry matter production and partitioning in groundnut was studied under adequately irrigated and simulated drought treatments. The study was conducted utilising twenty selected groundnut genotypes differing in their transpiration efficiency and was repeated with seven selected genotypes in the second season. Specific leaf area (SLA) and carbon isotope discrimination (CID) exhibited significant positive relationship indicating that specific leaf area can be utilised as a surrogate to CID. Specific leaf area was negatively related with transpiration efficiency, while it was positively related with partitioning suggesting that selection for low SLA might result in production of more dry matter with minimal influence on pod weight.

Key words: Carbon isotope discrimination, dry matter, groundnut, specific leaf area.

INTRODUCTION

Carbon isotope discrimination (CID) \vas show11 to be strongly related to transpiration use efficiency in groundnut genotypes (Hubick et a!.. 1986: Nageswara Rao eta!., 1993; Wright eta!., 1988). Specific leaf area (SLA), an easily measurable trait, v-.·as identified as a surrogate trait to carbon isotope discrimination· in groundnut (N ageswara Rao and Wright I 994: N ageswara Rao etal., 1995). Field studies examining the relationships of these traits with other yield contributing factors are necessary to utilise these traits for developing moisture stress tolerant cultivars. A positive association between SLA and HI reported by earlier studies (Wright et a!., 1988; 1993) suggests that selection for low SLA might result in production of more TOM than pod yield.

MATERIALS AND METHODS

The field experiments were conducted at the dry land fann of the Regional Agricultural Research Station,

lndianJ. Plant Physiol., Vol. 4, No.3, (N.S.) pp. 161-166 (July-Sept., 1999)

Timpati, A.P. ( 13

°

N latitude, 79° E longitude and altitude of 182.9M from MSL), during the rainy seasons of 1993 and 1994. The soils of the experimental field were typical red sandy loams, low in organic carbon, low to mediurr in available phosphoms, medium to low in available potassium with slightly acidic soil reaction. The water holding capacity of the soils was low with PWP of 5% and FC of 12-14%. Twenty selected groundnut genotypes differing in their water use efficiency were utilised for the study in 1993, and seven among these genotypes \vere used for the 1 994 experiment. The number of genotypes were reduced in the 1994 due to inclusion of moisture depletion studies which required larger plot size and the limitation of space in rain out shelters. Each genotype was grovm under two-moisture regimes i.e. irrigated (T₁) and

simulated drought (T₂) utilising rain out shelters. The

experiment was replicated thrice with irrigation regimes as main treatments and genotypes as sub treatments with a split plot design. In the irrigated treatment (T) irrigation was given once in four days by replacing 80% of

M. ASALATHA eta/.

cumulative pan evaporation (CPE) taking into account the rainfall received during the period. In simulated drought (T

2) moisture stress imposed between 40 and 80

days after sowing (DAS) by replacing 25% of the CPE once in four days. During the rest of the crop growth period T~ received normal irrigation like that ofT₁. Each

genotype was planted in three rows of 4m length with 30 em row spacing and 10 em intra-row spacing. Sampling

for specific leaf area was done at 40, 70 and 90 DAS utilising the Jrd or 4111 leaf from the tip on the main axis as

per Rao et al. (1995). The samples from the 70 DAS sampling were utilised for analyses of carbon isotope discrimination. Samples '"ere dried, powdered and sieved through a l 00 11m sieve and analysed for CID at the Research school of Biological sciences, Canberra, Australia as described by Hubick et a!., (1986).

TABLE I : Specific leaf area ( cnr2_g.·1

), carbon isotope discrimination and transpiration efficiency (glkg·1) of different groundnut genotypes

as int1uenced by irrigation treatments ( 1993 ).

Genotype

ICG 476

ICG 221

ICG 1697

ICG 2716

iCG 2738

ICG 3704

ICG 4790

ICG 5305

ICGV 86635

iCGV 86707

iCGV 86742

ICGV 86754

!CGV 87354

ICGV 87358

ICGV 86031

ICGV 86644

ICGS 76

TMV2 NLM

TPT-1

K 134

Mean SLA 197.4 172.5 161.5 168.5 164.9 182.9 160.0 190.0 172.5 164.5 173.7 142.6 174.1 143.8 118.4 160.9 178.9 137.8 153.3 175.2 165.7 S.E

]\-fain reatments I .16

Subtreatments 0.95

Interaction effects I .64

162 172.6 168.3 13l.l 139.6 151.4 152.6 151.7 162.5 154.3 148.0 147.3 132.1 164.9 138.8 115.4 153.3 159.8 129.2 143.1 145.6 148.0 3.15 1.88 3.25 mean

185 ()

170.4 146.3 154.1 158.2 167.8 155.9 176.3 163.4 156.3 160.5 137.4 169.5 141.3 116.9 157.1 169.4 133.5 148.2 160.4 CID 21.40 2l.l7 2l.l0 20.37 20.93 21.07 20.17 20.90 20.70 20.90 20.20 20.90 20.93 20.16 19.10 20.70 20.27 19.90 20.30 21.00 20.61 S.1·: 0.052 0.63 1.09 20.60 20.67 20.37 19.40 20.47 20.()7 19.43 20.30 19.70 20.23 20.10 20.53 20.20 19.93 19.40 20.10 19.87 19.00 19.50 19.90 19.99 0.14 1.25 2.16 Mean 21.00 20.92 20.74 19.89 20.70 20.57 19.80 20.60 20.20 20.57 20.15 20.72 20.57 20.05 19.25 20.40 20.07 19.45 19.90 20.45 2.53 2.78 2.87 2.91 2.82 2.88 2.8ti 3.03 3.03 2.95 2.81 3.27 2.82 3.36 3.61 2.92 2.93 3.62 2.72 2.45 2.96 S.E TE 0.036 0.052 0.0891 2.68 2.94 3.60 3.45 2.8ti 3.0ti 3.30 3.03 3.36 3.00 2.99 3.49 3 03 3.46 3.67 3.10 3.10 3.46 3.03 3.03 3.18 CD(ri\5% 0.099 0.102 0.177 mean 2.61 2.86 3.24 3.18 2.84 2.97 3 08 3.03 3.20 2.98 2.90 3.38 2.93 3.41 3.64

3 02 3 02

3.54

2.88

2.74

Transpiration efficacy (TE) was estimated as per Wright

et al., (1995) utilising the SLA values recorded in the study. The procedure involves the following steps for estimating the transpiration efficiency.

l) TE - K/(ei-ea) where K is the constant of proportionality and (ei-ea) the vapour pressure deficit (VPD).

2) K = 1.44-0.53

(.M

being the relationship ofK with actually measured Ll, where Ll is the carbon isotope discrimination.

3) Ll = 0.03 (SLS) + 14.0 being the relationship of Ll

with actual SLA values.

RESULTS AND DISCUSSION

Specific leaf area and carbon isotope discrimination values >vere higher and transpiration efficiency lower under adequately irrigated treatment (T) compared to simulated drought treatment (T) in both the years of study (Tables I and II). Specific leaf area varied from

116.9to 195.5 cm·2_{g., amongthegenotypestested. whereas}

the transpiration efficiency ranged from 2.21 to 3.64 g. kg·1 . _{Irrespective of the irrigation treatment ICGV 86031}

and TMV2NLM had lower SLA, CID values and higher TE compared to the ICG476. The TE of these genotypes was higher by 27 to 32% compared to ICG 476. The total dry matter production and pod yield were higher under T ₁ compared to T ₂. The groundnut genotypes tested exhibited

large variation in total dry matter production ( 455 to 1102 g. m·2

) and pod yield (167.0 to 292.5 g.m-2) The specific

leaf area of the genotypes (Fig. 1) had a significant positive relationship with CID under both T₁ and T₂• SLA

exhibited a strong negative relationship with TOM (Fig. 2) under T₁ and T₂. However, SLA had a significant

positive relationship with pod yield under only T₁• In T 2

the relationship, though positive, was non significant.

In groundnut many studies have shown negative relationship of CID with TE and TDM (Hubick et a!., 1986, 1988: Hubick 1990: Wright eta!., 1988, 1994). Subsequently it was shown that specific leaf area, an easily measurable trait has a strong positive relationship with CID and can serve as a surrogate to the CID \Vhich

TABLE II : Specific leaf area ( cm'g·' ), carbon isotope discrimination and transpiration efficiency ( glkg·') in groundnut genotvpes as affected by irrigation treatments ( 1994 ).

SLA CID TE

Genotype T, T. mean T, T. Mean T l T. mean

ICG 476 200.0 191.0 195.5 19.67 19.67 19.67 2.15 2.27 2.21

ICG 221 174.0 169.0 171.5 1R.76 1R.66 18.71 2.52 2.73 2.63

ICG 1697 155.0 154.0 154.5 18J)6 17.75 17.91 2.78 2.79 2.97

ICGV 86635 176.0 163.0 169.5 1R.87 17.96 18.42 2.47 2.66 2.57

ICGV 86031 126 () 127.0 126.5 18.13 17.74 17.94 3.18 3.18 3.18

TMV2NLM 122.0 118.0 120.0 17.40 17.56 17.48 3.25 330 3.28

Mean 159.3 154.1 18.54 18.16 2.78 2.85

S.E CDI{/15% S.E CDI{/15%, S.E C.D.(Zi>5%

Mainreatments 0.89 2.47 0.44 1.22 0.013 0.037

Sub treatments 1.00 2.03 0.61 1.24 0.009 0.018

Interaction effects 1.73 3.52 1.06 2.15 0.158

o.cm

M. ASALATHA eta/.

TABLE III: Total dry matter production and pod yield (g. m') of groundnut genotypes as aflected by irrigation treatments ( 1993). SLA

T, T,

ICG 476 600.00 465.8

ICG 221 770.8 681.6

ICG 1697 1048.3 1004.1

ICG 2716 865.0 851.6

ICG 3704 1022.5 829.1

ICG 4790 829.1 710.8

iCG 5305 981.6 891.6

1CGV 86635 743.3 575.8

iCGV 86707 859.1 805 ()

iCGV86742 826.6 771.6

ICGV 86754 972.5 856.6

ICGV 87354 932.5 717.5

ICGV 87358 1040.0 935.8

ICGV 860311 1012.5 905.8

ICGV 86644 1032.5 895.0

ICGS 76 864.1 644.1

TMV2NLM 960.0 742.5

TPT-1 910.0 742.5

K 13--t 684.2 641.6

Mean 899.1 735.8

S.E C.DI(/:5%

Main reatments 11.22 75.23

Sub treatments 12.44 59.49

Interaction etTects 21.56 103.05

requires the use of mass spectrometer. (Nageswara Rao and Wright 1994; NageswaraRaoetal., 1995). Nageswara Rao and Wright ( 1994) have observed consistent relationship (negative) between CID and SLA across locations and genotypes in groundnut. The negative relationship between CID and TDM is due· to the differences in photosynthetic capacity of genotype. This was in turn supported by their observation on the specific leaf nitrogen, which was negatively correlated with CID.

164

Pod yield

mean T, T, Mem1

532.9 229.0 146.6 187.8

726.2 307.5 277.5 292.5

1026.9 252.7 232.5 242.6

858.3 228.3 215.0 221.7

925.8 298.3 260.0 279.2

770.0 252.6 246.5 249.6

936.6 272.5 252.5 262.5

659.6 291.3 275.8 283.6

832.1 259.3 241.1 250.2

799.1 264.1 239.1 251.6

914.6 246.2 242.5 2444

825.0 280.0 231.6 255.8

987.9 237.6 215.0 226.3

958.8 215 () 205.0 210.0

963.8 250.0 279.1 264 (,

754. I 289.1 303.3 2'.!6.2

85!.3 215.0 195.0 255.0

826.3 248.0 218.0 233.0

662.9 2fi2.0 251.6 250.8

257.5 238.6

S.E C.D.@5%

188 7.39

5.53 15.50

9.59 26.85

Most of the variation in CID in groundnut genotypes was ascribed to variation in Rubisco (Nages,vara Rao eta!, 1995). A decline in Rubisco and the photosynthetic activity has been shown with leaf age (Evans, 1996: Cmmor et a!., 1993). Hence the position of leaf for analyses of CID or SLA is important. The present study that utilised a large number of genotypes confirms these results. There was significant positive relationship bet\\een SLA and CID, and negative association between SLA and

TABLE IV : Total dry matter production and pod vield (g. m') in groundnut gcnotvpes as affected by irrigation treatments (1994 ).

TDM

T, T,

ICG 476 527.0 383.3

ICG 221 1020.0 956.0

ICG 1697 1187.0 1017.0

ICGV 86635 1110.0 924.0

ICGV 86031 975.3 904.0

TMV2NLM 1169.3 1108.0

ICGS 76 786.0 886.3

Mem1 986.0 886.3

S.E C.D@5%

Mainreatments 21.86 94.06

Sub treatments 27.90 57.59

Interaction etTects 39.45 81.42

TOM (Figs. 1, 2). I is evident from the present study that it is possible to identify genotypes with high TE by screening for SLA. The positive relationship of SLA with pod yields in T₁ and positive trend of relationship in T::. though non-significant pose problems in breeding for genotypes with high TE and high pod yield. Positive relationship of SLA with pod yield means that the genotypes \vith lmv SLA are poor in partitioning. Such observations have been reported by other \Yorkers in

22~~~---,

~

21

8

20

19

•

18 L _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ j

100 150 200 250

SLA(cm-21g.)

20 r - - - ,

§ ₁₉ T2("94) ~

18 ~·

17L---~ 100 120 140 ~60 180 200 220

SLA1cm-2/g)

Fig. 1. Relationship between SLA and CID (,'\ x 10') in groundnut nenotypes under adequately irrigated and simulated

drought treatments.

IndianJ. Plant Physiol., Vol. 4, No.3, (N.S.) pp. 161-166 (July-Sept., 1999)

Pod yield

mean T, T, Mean

455.0 197.0 137.0 167.0

988.0 318.0 237.0 277.5

1102.0 257.0 230.0 243.5

1017.0 223.0 197.0 210 0

929.7 210.0 132 () 171.0

1138.7 230.0 167.0 198.5

936.0 282.0 228.0 255.0

936.0 282.0 228.0 255.0

S.E C.D.@5%

1310 36.70

18.53 51.90

20.37 57.00

groundnut (Wright eta/., 1988: 1993). Development of low partitioning lines will have a yield cost particularly when droughts do not occur. However. in some of the screening studies conducted at this station genotypes like TAG 24. TG26 and TCGS 320 were identified as possessing moderately high levels of TE with good partitioning. In a recent study on the genetic analyses of these trials Jayalakshmi eta!., ( 1998) have observed no significant relationship between TE and pod yield in F-3

1000

N

t

~ 800

~

.. ..

T1 ('93J

600 ~---~

-;oo 150 20C

1100

120 140 160 200 SLA (crn-2. g.)

Fig. 2.Relationship between SLA and TDM in groundnut genotypes under adequately irrigated and simulated droughts.

M. ASALATHA et a/.

material indicating the possibility for concurrent improvement of both the traits.

ACKNOWLEDGEMENTS

The authors acknowledge the financial support from the ACIAR-ICRSAT-ICAR Collaborators.

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